[gcc r15-2737] vect: Allow unsigned-to-signed promotion in vect_look_through_possible_promotion [PR115707]

[Feng Xue via Gcc-cvs]

https://gcc.gnu.org/g:3c089ee5d5a86cab0b27c69b96c4354c496520ac

commit r15-2737-g3c089ee5d5a86cab0b27c69b96c4354c496520ac
Author: Feng Xue <f...@os.amperecomputing.com>
Date:   Mon Aug 5 15:23:56 2024 +0800

    vect: Allow unsigned-to-signed promotion in 
vect_look_through_possible_promotion [PR115707]
    
    The function fails to figure out root definition if casts involves more than
    two promotions with sign change as:
    
    long a = (long)b;       // promotion cast
     -> int b = (int)c;     // promotion cast, sign change
       -> unsigned short c = ...;
    
    For this case, the function thinks the 2nd cast has different sign as the 
1st,
    so stop looking through, while "unsigned short -> integer" is a nature sign
    extension.
    
    2024-08-05 Feng Xue <f...@os.amperecomputing.com>
    
    gcc/
            PR tree-optimization/115707
            * tree-vect-patterns.cc (vect_look_through_possible_promotion): 
Allow
            unsigned-to-signed promotion.

Diff:
---
 gcc/tree-vect-patterns.cc | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
index 4674a16d15f4..b2c83cfd2190 100644
--- a/gcc/tree-vect-patterns.cc
+++ b/gcc/tree-vect-patterns.cc
@@ -434,7 +434,9 @@ vect_look_through_possible_promotion (vec_info *vinfo, tree 
op,
             sign of the previous promotion.  */
          if (!res
              || TYPE_PRECISION (unprom->type) == orig_precision
-             || TYPE_SIGN (unprom->type) == TYPE_SIGN (op_type))
+             || TYPE_SIGN (unprom->type) == TYPE_SIGN (op_type)
+             || (TYPE_UNSIGNED (op_type)
+                 && TYPE_PRECISION (op_type) < TYPE_PRECISION (unprom->type)))
            {
              unprom->set_op (op, dt, caster);
              min_precision = TYPE_PRECISION (op_type);